This invention relates to a mine stopping, a method for its installation and to a kit of components for use in the method of installing the stopping.
Stoppings are walls or partitions which are constructed and positioned to direct fresh air into selected areas of the mine. Areas where there are personnel working are required to be properly ventilated. In order to achieve this the stoppings need to be impermeable to air.
Stoppings have been previously constructed from hollow concrete blocks either dry stacked or wet laid, i.e. cemented in place. The stoppings, are usually made airtight by applying a non-porous coating or layer to the surfaces and the various areas of abutment. The usual technique involves trowelling over the surface and abutment areas with cementitious mortars based on Portland cement/sand powder blends mixed with water.
The use of mortars, including those which are premixed with water and which are known in the art as ready-to-use mortars has been found to be limited by their inability to set under wet or high humidity conditions where drying cannot take place.
U.S Pat. No. 5,165,958 describes a solution to this problem and discloses a process for sealing mine stoppings in wet or humid conditions employing a ready-to-use mortar comprising first and second components, the first component comprising an alkali metal silicate solution and a non reactive filler and the second component being essentially a solution of a reactant for the alkali metal silicate.
The construction of mine stoppings from concrete blocks with subsequent application of mortar is time consuming and labor intensive. This problem is addressed in U.S. Pat. No. 4,096,702 which describes a mine stopping formed by employing a wire mesh and applying to the wire mesh a plaster or cement.
Further, Patent Application No. W085/04444 describes the formation of a mine stopping by spraying a cementitious material onto a steel mesh. The inventive step is to tension the mesh by means of steel cables in order to prevent sagging which can result in grout being dislodged from the mesh.
The installation of stoppings by these previously described methods is nevertheless time consuming and it is highly desirable to be able to reduce the installation time. It has been found by the present inventors that by the use of a critical size of mesh an effective stopping can be prepared by applying the mortar to the screen from one side only. At these critical mesh sizes the mortar is able, when applied by spraying, to penetrate the mesh to a small degree thereby causing the mesh to become well embedded in the mortar and result in an effective stopping.
In a preferred embodiment of the invention employing a steel mesh, a fire resistant stopping can be prepared by spraying the mortar from one side only.
According to the present invention a method for installing a stopping in a mine opening comprises the steps of: (a) securely fixing in the mine opening a screen mesh having a size of about 2 to 24 mesh [preferably about 10 to 20 mesh, most preferably about 12 to 16 mesh], (b) applying a ready-to-use mortar to the screen to form a coating on the screen; and (c) continuing the application of the mortar until the stopping is airtight.
To achieve an airtight coating the thickness of coating will usually be at least about {fraction (1/32)} of an inch (0.08 cms) and may conveniently be at least {fraction (1/16)} of an inch (0.16 cms). The thickness of the mortar coating is conveniently between about xc2xc to 2 inches (and preferably substantially uniform in thickness) although thicknesses greater than this may be used.
The Screen.
The screen is intended to support the mortar while it sets and thereafter. The screen can be in the form of a mesh. The mesh may be in the form of a perforated sheet e.g. a metal sheet with holes punched through or in the form of an expanded metal. However a woven mesh (particularly one made of steel wire) is preferred because of its ease of attachment to the mine walls and floor and because it can be supplied in rolled up form as a cylinder. Desirably the screen has a tensile strength of at least about 150 lbs/inch2 preferably at least about 200 lbs/inch2, and most preferably at least about 250 lbs/inch2.
The mesh may be made of a plastics material such as a polyolefin plastics material, e.g. polypropylene, polyester or polyamide. Alternatively the mesh can be made of glass fiber or metal, such as steel.
Preferably the screen is of sufficient gauge of mesh that when a screen measuring about 8 feet by 4 feet is fixed in the mine opening with attachment points spaced at intervals of about 12 inches it can withstand a pressure of at least 39 pounds per square foot according to the test laid down in ASTM E72 before the mortar is applied
The Mortar.
The mortar is preferably a ready-to-use mortar and can conveniently be non-hydraulic, i.e. one that sets by drying. Preferably the mortar is non-cementitious. Ready-to-use mortars are supplied in sealed containers containing the required amount of water. The mortar may be silicate based, for example, as described in U.S. Pat. No. 5,165,958 (the disclosure of which is incorporated by reference herein) or a cementitious mortar which contains a retarder and a polymer in an amount to provide flexibility and which is mixed with an accelerator at the point of use.
The mortar may be any cementitious mortar mix, shotcrete, gunite, any ready-to-use mortar, or other substance such as a polyester, epoxy or polyurethane mortar setting by means other than hydration, or any mortar that allows the backing to meet the requirements of 30 CFR subpart D sections 75.300 et seq as interpreted by MSHA.
Flexible mortars may be used, for example those containing 3 to 20% by weight, based on the total weight of mortar, of polymer.
The mortar may be a fast-setting mortar and may also be capable of setting under wet or humid conditions. Such mortars are described in U.S. Pat. Nos. 5,165,958 and 5,330,785 (the disclosures of which are incorporated by reference herein).
The mortar is conveniently provided in the form of two components to be mixed. One component may comprise an alkali metal silicate solution and a non-reactive filler and the second component may comprise a solution of a water miscible reactant for the alkali metal silicate.
Preferably the alkali metal silicate is sodium or potassium and preferably the SiO2 to M2O mole ratio is from 2:1 to about 4:1 where M represents the alkali metal and the silicate solution has a solids content in the range of 10 to 60% by weight, preferably about 30 to 40% by weight (the remainder being water), and most preferably about 36%. Also, potassium silicate, as defined hereinabove, may be used.
The fillers used should, as stated above, be non reactive and compatible with the silicate solution in order to provide a long term shelf life. Suitable fillers are calcium carbonate (e.g. limestone), mica, cellulose fiber, other reinforcing non-reactive fibers, clay, kaolin, pigments, and dispersing agents.
The water miscible or water soluble reactant to initiate gel formation may be any weak acid or acid salt or ester or ester blend that hydrolyses to release acid. Such esters may include diacetin, triacetin, and/or blends of commercially available dibasic esters known as D.B.E. comprising the methyl esters of adipic, glutaric, and succinic acids or other materials of the formula R1OOC(CH2)nCOOR2 wherein R1 and R2 may be the same or different alkyl groups containing from 1 to 20 carbon atoms, preferably 1 to 6 carbon atoms, and n is 2, 3, or 4, together with glycerol or propylene glycol to aid solubility of the ester.
Application of the Mortar.
The mortar may be applied by hand by a suitable mason""s tool, such as a trowel. Preferably however the mortar is applied by spraying. A pump may be used for effecting the spraying for example a progressive cavity pump, or a piston pump.
Spraying is conveniently carried out using a spray nozzle under conditions such that the velocity of the material leaving the nozzle is not greater than about 150 feet/second and is typically in the range of about 80 to 115 feet/second. These nozzle velocities, which are achieved by carrying out the spraying operation without compressed air, reduce the tendency of the screen to flex and thereby makes the application easier.
Conveniently the distance of the nozzle from the mesh is from about 2 to 15 feet, preferably from about 3 to 12, and most preferably from about 4 to 10 feet.
Conveniently the spraying is effected using a small size nozzle e.g. one about xe2x85x9 inch in diameter. The nozzle may be in the form of a slit which in use opens to a size equivalent to about xe2x85x9 inch. Preferably no sand or coarse material is used.
It is not, in all cases, essential that the mortar sets, although it is preferred that the mortar does so. In preferred forms of the invention a mortar will be used that will set under the conditions at the installation site.
Although adequate stoppings can be obtained by spraying from one side only, it is within the scope of the present invention to spray both sides if this is desired. When the mesh is made of a combustible material, e.g. polypropylene plastics material, it may be convenient to spray both sides of the screen in order to obtain a fire resistant stopping. It is a feature of the present invention that when the mesh is made of a non flammable material, a fire resistant stopping can be prepared by spraying from one side only.
The screen is securely fixed before mortar application. By xe2x80x9csecurely fixingxe2x80x9d it is meant fixing the screen so that it will act as a support without specifically sagging or bending from the mortar applied to it. The term xe2x80x9cminexe2x80x9d as used herein means any underground working. The term xe2x80x9cstoppingxe2x80x9d as used herein means partitions which divide or separate air currents in mines. Stoppings may be used in construction of other ventilation control devices in mines, in particular xe2x80x9covercastsxe2x80x9d, xe2x80x9cundercastsxe2x80x9d or xe2x80x9cregulatorsxe2x80x9d. The term xe2x80x9cairtightxe2x80x9d is intended to be given its usual meaning in the mine stopping art. The term xe2x80x9cready-to-use mortarxe2x80x9d means a mortar to which it is not necessary to add further water. In some cases it may be necessary to add further material such as hardener and it may be advantageous to add further water but it is not essential to do so.
Mesh measurements as set forth herein are defined as the number of openings/inch from the center of the wires.
A support structure for the screen is preferably secured and tensioned by bolts or similar fastening means fixed to the roof and/or floor and/or side walls (ribs) of the mine. The screen is conveniently installed in the mine opening by fasteners attached to the roof, or floor, or side walls, or friction wedges between structural supports and the roof and/or floor and/or side walls of the mine opening. Preferably, the screen/support structure is attached directly to the roof and rib walls with nails, spads or similar fixing means. Additional strips of rough lumber or similar material may be used to assist in the attachment of the support to the previously attached rough lumber or directly to the walls or roof.
Alternatively there is first attached to the mine walls and/or roof and/or floor, bolting boards made of rough lumber. The support structure which has previously been cut to dimensions somewhat larger than the mine opening is then attached to the wood with nails or spads.
According to another aspect of the invention there is provided a kit of components for installing a stopping in a mine opening the kit comprises as a first component, a screen of mesh size of about 2 to 24 mesh [preferably about 10 to 20], for installation in the mine opening and receiving mortar and supporting said mortar; and, as a second component, a mortar [preferably a ready-to-use mortar] for application to the screen to provide the stopping. The kit may also include other components, such as fasteners. The term xe2x80x9ckitxe2x80x9d means a pack or container holding the screen and the mortar.
It is desirable to be able to employ a ready-to-use mortar for the preparation of mine stoppings because this enables the operation to be done more quickly, and also because there is a lack of readily available water in many mines. Ready-to-use mortars are supplied in sealed containers and when applied harden by air drying. It has been found according to the invention that there is a problem with ready-to-use mortars in that when they are applied to a mesh to prepare a mine stopping there is a risk of shrinkage cracking. It is a feature of the present invention that by the use of the critical size of mesh described above the problem of shrinkage cracking is avoided. This is particularly significant for a mine stopping where airtightness is required.